By default, the SSO login page opens in a new window. Selecting the check box in the SSO login and logout page section of the Authentication administration interface forces the SSO login and logout page to open in the current window.
Some SSO implementations have technical constraints that prevent the authentication window from working as expected. Indeed, the authentication window must be able to communicate with its "opener window." Some SSO implementations break (intentionally or not) the reference to this opener window. In this case, the authentication window is not able to communicate with its opener. The authentication window is not closed and displays Fluid Topics with the user recognized as authenticated.